1. Field of the Invention
The present invention generally relates to a metal structure of a multi-layer substrate and the manufacturing method thereof, and more particularly to a metal structure of a flexible multi-layer substrate and the manufacturing method thereof.
2. Description of Prior Art
A multi-layer substrate can be utilized for manufacturing a package substrate, a printed circuit board, a flexible package substrate or a flexible printed circuit for realizing miniaturization of all electronic products is an inevitable trend in this modern world. Particularly, a flexible multi-layer substrate can be utilized for manufacturing a flexible package structure to apply in kinds of products to meet miniaturization demands more efficiently. As the thickness of the flexible multi-layer substrate gets thinner, the routing density of the multi-layer substrate becomes higher. Accordingly, the requirements of the metal structure size of the flexible multi-layer substrate become smaller and more meticulous. Traditional flexible multi-layer substrates according to prior arts can only be manufactured with two or three layers. The thickness of each layer is about 50˜60 μm and the thickness of the metal layer is about 30 μm.
Please refer to FIG. 1, which depicts a diagram showing a bubble generated at a side of a metal structure of a multi-layer substrate according to prior arts. The multi-layer substrate according to prior arts can be flexible comprises a metal layer 100 and a dielectric layer 102 covering the metal layer 100. Generally, an etching or a build-up process is utilized to form the metal layer 100 of the flexible multi-layer substrate according to prior arts. When the metal layer 100 is employed as a metal line or a pad, the sectional appearance of the metal layer 100 shows a rectangular figure. A common problem which often occurs is that a bubble generated at the side the metal layer 100. As shown in FIG. 1, a phenomenon of bad adhesion or delamination in layers exists due to the bubble. As a result, a lower manufacturing yield of the flexible multi-layer substrate happens. Particularly, as the metal layer 100 becomes thinner as along as the thickness of the flexible multi-layer substrate gets thinner, the influence of the aforesaid phenomenon of bad adhesion or delamination in layers unavoidably turns to more obvious.
Please refer to FIG. 2, which depicts a diagram showing a metal structure of a multi-layer substrate stripped off with a ball mount due to an external force according to prior arts. As aforementioned, as the metal layer 100 is employed as a metal line or a pad, the sectional appearance of the metal layer shows a rectangular figure. As the metal layer 100 is utilized as a metal layer for package of an IC (Integrated Circuit), the dielectric layer 102 covering the metal layer 100 above is going to be opened a hole and a metal material 106 is formed in for connecting with the solder ball mount 108. As previously mentioned, the flexible multi-layer substrate is utilized as a flexible package substrate or a flexible printed circuit. Generally, it is applied for a constantly bent device. Namely, when the flexible multi-layer substrate is bent, the metal layer 100 may be stripped off with the solder ball mount 108 due to a bending external force as shown in FIG. 2 because the bonding strength between the metal layer 100 and the solder ball mount 108 is too strong. Similarly, as the metal layer 100 becomes thinner as along as the thickness of the flexible multi-layer substrate gets thinner, the aforesaid stripped-off phenomenon unavoidably becomes more possible and happens more easily.
In conclusion, there is a need to develop a metal structure of a flexible multi-layer substrate and manufacturing method which is still valid for resolving the aforesaid problems when the thickness of the flexible multi-layer substrate is manufactured thinner and accordingly the metal layer also has to be thinner, wherein the metal structure cannot easily be delaminated or separated from the contacted, adjacent dielectric layers and a higher reliability of the metal structure can be achieved.